Fibers of glass and other thermoplastic materials are useful in a variety of applications including acoustical or thermal insulation materials. The common prior art methods for producing glass fiber insulation products involve producing glass fibers from a rotary process. A single molten glass composition is forced through the orifices in the outer wall of a centrifuge or spinner, producing primarily straight glass fibers.
An improvement over conventional glass fibers, which are usually straight fibers, is the use of fibers which are curly (helical) or irregular in shape. These fibers can be made by joining two distinct glass streams, referred to as the A glass and the B glass, and centrifuging the dual glass stream into a curly (helical) fiber, or into an irregular dual-glass fiber. For purposes of this patent specification, in using the terms "glass fibers" and "glass compositions", "glass" is intended to include any of the glassy mineral materials, such as rock, slag and basalt, as well as traditional glasses. Thermoplastic materials and thermoplastic fibers include, in addition to glass and other mineral fibers, fibers from polymer materials, such as polyester fibers and polypropylene fibers.
Stalego in U.S. Pat. No. 2,998,620 discloses curly (helical) glass fibers of bicomponent glass compositions. Stalego teaches producing staple curly fibers by passing two glass compositions of differing thermal expansivity through the orifices of a spinner. The glasses are extruded as a dual glass stream in aligned integral relationship such that the fibers curl naturally upon cooling due to the differing thermal expansivity. Stalego discloses a spinner having vertically aligned compartments around the periphery of the spinner, with alternate compartments containing the different glasses, separated by vertical baffles. Stalego further teaches that an orifice wider than the baffle is to be drilled where the baffle intersects the spinner peripheral wall. Since the orifice is wider than the baffle, the orifice is in communication with both of the vertical compartments on either side of the baffle, and both the A glass and the B glass will exit the spinner from the orifice, forming a dual glass stream. There is a need for improving the delivery of dual glass streams of molten glass or other thermoplastic materials to form curly or irregularly-shaped glass or other thermoplastic fibers.